In recent years much research work has been devoted to solar cells, and this has i.a. entailed an increased interest in solar cell modules of the above-mentioned type. These modules have a significant advantage, since the active area of the module is determined by the area of the concentrator, and such a concentrator may e.g. be a lens or a mirror. The concentrator is expediently a Fresnel lens, since these can be made of a plastics material, thereby minimizing the manufacturing costs. At the same time, Fresnel lenses have a significant advantage, since the lens thickness is reduced, so that the concentrator is very light in this case. When the optical principal axis of the concentrator is directed to the sun, the latter will be imaged in the focal point of the concentrator. Light energy having a very high intensity level will be concentrated around the focal point, so that the solar cell, which is to convert this light energy into electric energy, must be of a very high quality, e.g. made of monocrystalline silicon or gallium arsenide. For best possible utilization of the area of this solar cell, a second optical element is usually positioned in front of the solar cell, said optical element being constructed such that the light energy is distributed evenly over the active areas of the entire solar cell. A plurality of solar cell modules of this type are then assembled to provide a solar cell panel of matrix shape. Since, owing to the imaging properties of the concentrator, the solar cells only receive light energy which is propagated along the optical principal axis of the concentrator, the panel must be mounted on a device so that the panel can follow the travel of the sun across the sky. This technique is known and described in e.g. "Conference Record of The Twentieth IEEE Photovoltaic Specialists Conference, 1988, Volume II", pages 1138-1143 by Don Carroll.
Solar cell panels of this type operate satisfactorily when the optical principal axis of the concentrator is directed to the sun. In cloudy weather the visual field of the panel does not contain a powerful light source in the form of the sun, since the incident light will be in the form of diffuse light from all directions. The advantages of the concentrator by concentrating light from an area corresponding to e.g. 500 times the area of the solar cell, are thus gone. A solar cell panel of that type is therefore useful only in regions where a reasonable number of sunshine hours per day is certain with some statistical probability, it being thus certain that the solar influx is mainly direct influx. Therefore, it is not attractive to use such a solar cell panel in large parts of the world, since it must be considered unreliable depending upon the light conditions.